现行中等师范学校《生物学》（试用本）第二册102页,有这样一段叙述:“众所周知,鸵鸟的蛋有170×135毫米这样大,它是世界上最大的细胞。”旁边画出了鸵鸟蛋、鸡蛋、蜂鸟蛋、人卵进行细胞大小的比较图。我们认为这样的比较是错误的。因为,鸟类的蛋结构比较特殊,从它们的结构组成和发生过程来看,与一般的细胞都有所不同。下面以鸡蛋为例来看看蛋的结构和发生过程。 一、鸡蛋的结构 鸡蛋最外面有坚硬的石灰质蛋壳,其内部有两层壳膜和比较厚的蛋白质。这些结构除保护卵子免遭损伤外,并能防止水分过分地蒸发。 蛋壳由三层组成:最内层为乳头层,由小球形的石灰结晶组成;中间是最厚的海绵层,占蛋壳厚的2/3,由石灰结晶体编织而成,壳的色素就集聚在此层的外部;最外层是极薄的角质层,由白质和分散的脂肪球所组成。整个蛋壳上有许多小孔沟通,小孔在气室处较多,供胚胎呼吸 In the second volume of the current “Secondary” of the Normal School for Normal Schools (trial paper), page 102, there is a paragraph saying: “As we all know, an ostrich egg is as large as 170 x 135 mm. It is the largest cell in the world.” Ostrich eggs, eggs, hummingbird eggs, and human eggs are used to compare cell sizes. We think this comparison is wrong. Because the egg structures of birds are special, they differ from the general cells in terms of their structural composition and their occurrence. Take the egg as an example to look at the structure and process of the egg. First, the structure of the egg The egg has a hard outer limestone shell, which has two layers of shell membrane and a relatively thick protein inside. These structures protect the eggs from damage and prevent excessive evaporation of water. The eggshell consists of three layers: the innermost layer is the nipple layer, composed of small spherical lime crystals; in the middle is the thickest sponge layer, which accounts for 2/3 of the thickness of the eggshell, which is woven from lime crystals and the pigment of the shell. Clustered on the outside of this layer; the outermost layer is a very thin cuticle consisting of white matter and dispersed fat globules. There are many holes communicated throughout the eggshell, and there are more holes in the air chamber for the embryo to breathe